Biomass fuels are commonly used in burn processes for generation of heat and energy. One of the most important biomass fuels is wood. However, different biomass fuels generate different amount of heat and different amount and type of residuals after burning. Great deviations exist also for different types and qualities of wood. This makes it difficult to control a burning or combustion process effectively.
The effective thermal value of a specific biomass fuel can be determined relatively precisely if the moisture content and ash content for the biomass fuel is known. However, heretofore, fast and accurate estimation of both moisture content and ash content have been difficult to achieve in practice.
Ash from biomass, such as wood, typically comes from the minerals present in the structure of e.g. trees and shrubs in addition to any soil contamination and other contaminations. Properties of wood ash depend on a variety of factors including the type of tree or shrub, the part of the tree or shrub (bark, wood, leaves), type of waste (wood, pulp, or paper residue), type of soil and climate and conditions of combustion.
Agricultural residues typically generate significantly more ash than woody biomass. Typically, the ash content in wood is about 0.5 percent, whereas it is 5 to 10 percent in diverse agricultural crop materials, and up to 30 to 40 percent in rice husks and milfoil.
The composition and amount of ash affects the biomass behavior under the high temperatures of combustion and gasification. For example, melted ash may cause problems in both combustion and gasification reactors. These problems can e.g. be clogged ash removal systems caused by slagging ash, fouling of burners and boilers from ash deposition, and severe operating problems in fluidized bed systems. When wood is combusted alone, ash deposition is not typically a problem because combustion temperatures are likely to be low. However, when biomass is co-fired with coal, combustion temperatures are considerably higher and may reach a level where slagging could occur.
There is therefore a need for a fast and accurate method and system for determining ash content of a biological material, and in particular for biomass fuels, which can e.g. be used directly by people in field work operation, be used in automated processes, and the like.